Method and apparatus for enhanced performance in a system employing convolutional decoding

Abstract

The invention comprises a method and apparatus for decoding an incoming symbol stream comprised of a plurality of known missing symbols. Within the incoming symbol stream, those symbols corresponding the known missing symbols are replaced with a first set of values to create a modified symbol stream. The modified symbol stream is convolutionally decoded to produce a first decoded information bit stream. An error detection mechanism is performed on the first decoded information bit stream to determine a “pass” or “fail” indication. If the error detection mechanism produces a “fail” indication, a second set of values replaces the known missing symbols to produce a second modified symbol stream. The second modified symbol stream is convolutionally decoded to produce a second decoded information bit stream. The error detection mechanism is performed on the second decoded information bit stream. If the error detection mechanism produces a “pass” indication, the second decoded information bit stream is passed to the next processing layer. Additional repetitions can be completed until an error free decode is obtained or a predetermined number of attempts is completed without a “pass.”

What is claimed is:  
     
       1. A method of decoding an incoming symbol stream comprising a first plurality of bits, the first plurality of bits originating from an original plurality of bits from which ones of said original plurality of bits were deleted, comprising the steps of: 
       filling said first plurality of bits with a first set of replacement values to replace the deleted ones of said original plurality of bits to generate a first reconstructed approximation of said original plurality of bits;  
       convolutional decoding said first reconstructed approximation of said original plurality of bits to produce a first decoded information bit stream;  
       performing error detection on said first decoded information bit stream;  
       indicating whether errors are present in said first decoded information bit stream;  
       modifying the first set of replacement values with a second set of replacement values, different at least in part from said first set of replacement values to create a second reconstructed approximation of said original plurality of bits;  
       convolutional decoding said second reconstructed approximation to produce a second decoded information bit stream;  
       performing said error detection on said second decoded information bit stream; and  
       indicating whether errors are present in said second decoded information bit stream.  
     
     
       2. The method of claim  1 , further comprising, the steps of: 
       if errors are detected in the second decoded information bit stream,  
       repeating said modifying, convolutional decoding, performing and indicating steps until a maximum number of attempts is completed or an error free bit stream is detected.  
     
     
       3. The method of claim  1 , wherein said incoming symbol stream comprises soft decision data values. 
     
     
       4. The method of claim  1 , wherein said second set of replacement values comprises at least some small non-zero values. 
     
     
       5. The method of claim  1 , further comprising the step of re-encoding said first decoded information bit stream to produce a first re-encoded symbol stream and using the re-encoded symbol stream in a determination of at least some values within said second set of replacement values. 
     
     
       6. A method of decoding an incoming symbol stream, said incoming symbol stream comprising an original symbol stream comprising a first plurality of bits, the first plurality of bits comprising an original plurality of bits with ones of said original plurality of bits deleted, comprising the steps of: 
       filling said first plurality of bits with a first set of replacement values which replace the deleted ones of said original plurality of bits to create a first modified symbol stream;  
       convolutionally decoding said first modified symbol stream to produce a first decoded information bit stream;  
       performing error detection on said first decoded information bit stream; and  
       if errors are present in said decoded information bit stream, said method further comprising the steps of:  
       filling said first plurality of bits with a second set of replacement values to replace the deleted ones of said original plurality of bits, said second set of replacement values different, at least in part, from said first set of replacement values to generate a second modified symbol stream;  
       convolutionally decoding said second modified symbol stream to produce a second decoded information bit stream; and  
       performing said error detection on said second decoded information bit stream.  
     
     
       7. The method of claim  6 , further comprising the step of if errors are present in said decoded information bit stream, re-encoding said first decoded information bit stream to produce a first re-encoded symbol stream. 
     
     
       8. The method of claim  6 , wherein said incoming symbol stream comprises soft decision data values and wherein said first set of values is a set of erasure values and said second set of values comprises a set of at least one non-zero value. 
     
     
       9. The method of claim  8 , wherein a polarity of at least one value of said second set of values is determined based on the result of the first convolutional decoding step. 
     
     
       10. The method of claim  6 , wherein said step of performing error detection comprises the steps of: 
       calculating a received CRC value for said first decoded information bit stream;  
       comparing said received CRC value to an appended CRC value within said first decoded information bit stream;  
       failing said first decoded information bit stream if said appended CRC value does not match said received CRC value; and  
       passing said first decoded information bit stream if said appended CRC value matches said received CRC value.  
     
     
       11. A method of decoding an incoming symbol stream comprising a first plurality of bits, the first plurality of bits comprising an original plurality of bits with ones of said original plurality of bits overwritten with alternative bits, said method comprising the steps of: 
       receiving said incoming symbol stream;  
       replacing said alternative bits with a first set of replacement values to generate a first reconstructed approximation of said original plurality of bits;  
       convolutionally decoding said first reconstructed approximation to produce a first decoded information bit stream;  
       performing error detection on said first decoded information bit stream to ascertain whether errors are present in said first decoded information bit stream; and  
       replacing said alternative bits with a second set of replacement values to generate a second reconstructed approximation of said original plurality of bits if an error is detected.  
     
     
       12. The method of claim  11 , further comprising the step of removing the alternative bits from said incoming symbol stream. 
     
     
       13. The method of claim  12 , further comprising the steps of storing said alternative bits. 
     
     
       14. An apparatus for decoding an incoming symbol stream having a plurality of known missing symbols, said apparatus comprising: 
       means for replacing said plurality of known missing symbols with a first set of values to create a first modified symbol stream;  
       means for convolutional decoding said first modified symbol stream to produce a first decoded information bit stream;  
       means for performing error detection on said first decoded information bit stream;  
       means for re-encoding said first decoded information bit stream to produce a first re-encoded symbol stream if said first decoded information bit stream fails said error detection;  
       means for replacing said plurality of known missing symbols within the re-encoded symbol stream with a second set of values to create a second modified symbol stream;  
       means for convolutional decoding said second modified symbol stream to produce a second decoded information bit stream; and  
       means for performing error detection on said second decoded information bit stream.  
     
     
       15. The apparatus of claim  14 , further comprising: 
       means for re-encoding said second decoded information bit stream to produce a second re-encoded symbol stream if said second decoded information bit stream fails said error detection;  
       means for replacing said plurality of known missing symbols within said second re-encoded symbol stream with a third set of values to create a third modified symbol stream;  
       means for convolutional decoding said third modified symbol stream to produce a third decoded information bit stream; and  
       means for performing error detection on said third decoded information bit stream.  
     
     
       16. The apparatus of claim  14 , wherein said incoming symbol stream comprises soft decision data values and wherein said first set of values is a set of erasure values, said second set of values comprises a set of at least one small non-zero value and said third set of values comprises a set of at least one larger non-zero value. 
     
     
       17. The apparatus of claim  14 , wherein said incoming symbol stream comprises soft decision data values and wherein said first set of values is a set of erasure values and said second set of values comprises a set having at least one non-zero value. 
     
     
       18. The apparatus of claim  14 , wherein said plurality of known missing symbols carry a punctured sub channel. 
     
     
       19. An apparatus for decoding convolutionally encoded symbol data having a plurality of punctured symbols, said apparatus comprising: 
       a demodulator having a soft decision symbol output;  
       a depuncture logic having a symbol input in communication with said soft decision symbol output of said demodulator, said depuncture logic configured to replace said punctured symbols with at least one non-zero soft decision value, said depuncture logic having a modified symbol stream output;  
       a convolutional decoder having a symbol input in communication with said modified symbol stream output of said depuncture logic and having a decoded information bit stream output;  
       a processing unit having a data input in communication with said decoded information bit stream output of said convolutional decoder;  
       an encoder having a bit input in communication with said decoded information bit stream output of said convolutional decoder and a symbol output in communication with said symbol input of said depuncture logic; and  
       an error detection module in said processing unit, said error detection module configured to determine whether errors are present in said decoded information bit stream output of said convolutional decoder, said depuncture logic configured to successively replace said puncture symbols with alternate soft decision values until an error-free decoded information bit stream is detected or a maximum number of trials is reached.  
     
     
       20. The apparatus of claim  19 , further comprising: 
       a processing unit in communication with said depuncture logic, said processing unit configured to control the value to use for replacing said punctured symbols, said values selected from soft decision values.  
     
     
       21. The apparatus of claim  20 , wherein said depuncture logic comprises a multiplexer, and wherein said processing unit communicates replacement values to an input of said multiplexer.